Yes, there is. As much as there is with any medium. Letter can be burnt, voice mails can be erased, e-mails deleted. Even stone tablets can be broken.
and odds are he was blocking the harridan.
Why is she a harridan? And if he was "blocking her" how was she suppose to inform him?
The way you are setting it up aside from a formal summons there is no way she can "Prove" that he got notified without a response from him.
And how many guys respond when their casual sexual partner tells them that she is pregnant? Half maybe?
The law says she must inform him. She did. If they want to change the law so it defines more narrowly the way she must do so they can for the future but that would be expost facto in this case.
There is no denying that she did inform him, even he admits that.
The law also generally spells out what is acceptable service.
Facebook is not it. I laugh a million LOLs at those who say it has a permanent record, even like unto the classifieds that generally serve as legal notices. If I miss looking at Facebook even for a day, it takes 15 minutes of scrolling to see where to catch up. No, will not legally fly, and the court did the right thing, and now all citizens are put on notice.
Also I see no such “admission.” Probably granted arguendum.